But state Senator Katherine Clark of Melrose appeared to have the most cash stocked away, with more than $400,000 in the bank on June 30 after pulling in $228,000 in the quarter, according to her campaign.

Official fund-raising reports from the candidates are due to the Federal Election Commission in Washington by Monday, but their campaigns have given an early look at a key metric of how each is doing.

The mostly suburban Fifth Congressional District stretches from Winthrop to Woburn to Weston to Holliston. It is heavily Democratic so the winner of the primary will be the strong front-runner to take over as Markey’s successor.

State Representative Carl M. Sciortino of Medford raised $203,000 in the quarter and had more than $270,000 in his account on June 30, according to his campaign.

State Senator Karen Spilka of Ashland raised more than $200,000, and had over $200,000 in the bank at the end of last month.

State Senator Will Brownsberger of Belmont raised $130,000 and had $290,000 in cash on hand at the end of June.

Fund-raising is essential in all modern political campaigns, but the race for money is particularly important in what looks set to be a sleepy special election campaign for a seat in the House of Representatives. Each of the five declared candidates has a base of support, but needs to attract the attention of voters who do not know much about them.

It will take money to introduce themselves — whether through a door-by-door field operation, lawn signs, direct mail pieces, or television and radio advertisements. And they will have to make their case to an exhausted electorate, worn out by one political contest after another.

Markey defeated Republican Gabriel E. Gomez in a special election last month to fill the Senate seat that was held by John F. Kerry, who is now secretary of state.

Markey is set to be sworn in to the Senate on July 16. After his congressional seat officially becomes vacant, Governor Deval Patrick will set a date for the special election to fill it, probably in December. That means a probable October primary would be sandwiched between a high-wattage preliminary race for mayor of Boston in September and the deciding contest to replace Thomas M. Menino in November.